3GPP (3rd Generation Partnership Project) LTE-Advanced (Long Term Evolution Advanced) Work Item develops a relay node (hereafter referred to as RN) for deployment in a cellular network. One of the main objectives for deploying RNs is to enhance coverage area of a base station by improving throughput of a mobile station (user terminal) that locates in a coverage hole or far from the base station (see NPL1). Hereafter, a base station is referred to as BS or eNB (evolved Node B) and a mobile station or user terminal is referred to as UE (user equipment).
In the cellular network with RNs, eNB that can provide radio connection to a RN is called Donor eNB, which is hereafter denoted by DeNB. Note that, in this description, the terms eNB and DeNB are distinguished such that eNB is a base station without any RN connecting to it and DeNB is a base station with at least one RN connecting to it. The radio connection between the DeNB and RN is called a backhaul link (or Un interface) and hereafter, a RN “having a backhaul link connection with” a certain DeNB will be referred to as the RN “registered to” that DeNB. Moreover, the term DeNB-UE is used for referring to UE that establishes a radio connection with DeNB, and the term RN-UE is used for referring to UE that establishes a radio connection with RN. The radio connection between DeNB and DeNB-UE is referred to as DeNB-access link, and the radio connection between RN and RN-UE is referred to as RN-access link (or Uu interface). Currently, 3GPP RAN Working Groups (RAN WGs) are mainly considering a RN called Type1 RN that shares common radio resources among the DeNB-access link, RN-access link, and backhaul link. In order to prevent self-interference at the Type1 RN between the backhaul and RN-access links, both links are time-division multiplexed by semi-statically configuring time-domain radio resources called backhaul subframes, that only allow communication between DeNB and RN (see NPL2 and NPL3).
As shown in FIG. 1, it is assumed for simplicity that the cellular network is composed of different DeNB1 and DeNB2 each controlling different macro-cells (donor-cells) and multiple RNs, which may be registered to the same DeNB or registered to different DeNB1 and DeNB2. In this example, relay nodes RN1 and RN2 are registered to DeNB1 and DeNB2, respectively. The RN1 controls a relay-cell1 and mobile stations RN1-UE1 and RN1-UE2 and the RN2 controls a relay-cell2 and mobile stations RN2-UE1 and RN2-UE2. In downlink communication, it is further assumed that, when the RN1 and RN2 transmit data to their RN-UEs at the same time, interference between RN-access links occurs as shown by dashed lines in FIG. 1, causing the capacity of a RN to be limited.
In order to solve this problem, the backhaul subframe coordination method as in [NPL4] can be applied. In specific, NPL4 discloses the relay network in which the DeNB coordinates timing allocation for transmitting backhaul link data to each of the multiple RNs (hereafter referred to as backhaul subframe configuration applied at the RN) such that the backhaul subframe timings are differentiated. Therefore, each RN can have different timings compared with the other RNs, for receiving and transmitting the backhaul and RN-access link data, respectively, allowing the interference between RN-access links in the network to be reduced.